In recent years, with the ever expending commercial market of portable terminals such as smartphones, tablets or the like, demand for a semiconductor memory device such as a flash memory is on the rise, and an increase in volume of recorded data is also progressing. Miniaturization of the semiconductor memory device is indispensable to the high-capacity of the device. With the progress of miniaturization of the semiconductor memory device, for example, in a flash memory having a floating gate (FG) structure, the number of electric charges accumulated in the FG has been decreased up to a level of 100 or less. As such, if a slight defect exists in a tunnel insulation film, the electric charges may be drawn from the FG through the defect, which causes leakage of data. To address this, there is suggested a structure in which a plurality of nanodots is formed in an electric charge accumulation layer. In such a structure, since the electric charges are accumulated in each of the discrete nanodots, the accumulated electric charges are hardly drawn out, thus reducing the leakage of data. In the structure, the plurality of nanodots is formed on an insulation film by a self-alignment process.
On the other hand, as a typical method for forming wirings, electrodes or the like of a semiconductor device, a CVD (chemical vapor deposition) method is known. As a technique for forming a metal film using the CVD method, there is suggested a method which uses a ruthenium carbonyl (Ru3(CO)12) as a film-forming raw material, an argon gas as a carrier gas, and a hydrogen gas as a reduction gas. In addition, there is suggested another method which uses a ruthenium carbonyl as a film-forming raw material, and a carbon monoxide (CO) as a carrier gas. In a reaction system using the ruthenium carbonyl and the carbon monoxide, since impurity components included in the film-forming raw material are basically restricted as carbon and oxygen, it is possible to obtain a highly purified film. Also, there is suggested yet another method which uses a ruthenium carbonyl as a film-forming raw material, and performs an annealing process under a hydrogen-containing atmosphere after the film-forming process, thus reducing residual carbons in the film.
In addition, in forming a thin film using the CVD method, there is suggested a technique which adds an inhibitor such as ammonia or the like. In such a method, the inhibitor allows nuclei to be uniformly formed during a growth process of a thin film such as HfB2 film, thus obtaining a smooth thin film.
As mentioned above, in recent years, design rules of semiconductor devices are increasingly miniaturized. For example, nanodots used in a flash memory are increasingly required to be finely and evenly formed. In the conventional methods, although the plurality of nanodots is formed on the insulation film by the self-alignment process, if fine nanodots can be formed by the CVD method as a relatively general method, it is possible to decrease the number of processes, thus providing a wider range of applications.